Synthesis of Ti-Ni-O Modified Surfaces on Shape Memory Alloys for Biomedical Applications

Abstract Present paper investigates the relationship between the processing parameters of electrochemical anodization (EA) and the oxide morphology developed on cylindrical surface of 0.4 mm diameter wires of NiTi alloy. The synthesis was done by EA in fluoride based electrolyte by using aqueous solution of 9.34 wt.% H3PO4 and 0.5 wt.% HF. Several experiments were carried out at anodization potential of U = 20, 10, 5, 4, 3, 2 V for a duration of 10 minutes. Longer experiments of 30 min were done at a fine-tuned value of anodization potential of U = 3.5 V. Scanning electron microscopy (SEM and HR-SEM) was used to evaluate the morphology of the Ti-Ni-O oxide layers. The mass loss and the current evolution were analyzed in relation with the anodization results. By using anodization potential of 10 V and 20 V, current densities were of 15-62 mA/mm2 and the process that occurred was an etching one, leading to a mass loss of 4 - 12.5 %. Optimization of EA by fine-tuning the electrical parameters, i.e use of lower anodization potential of 3.5 V and 4 V, lead to current densities of 1 - 1.8 mA/mm2, and to the synthesis of Ti-Ni-O oxide with a well structured nanoporous morphology with pores’ diameter in the 20 - 140 nm range.